1. Technical Field
This invention relates generally to computers, and in particular, to modular expansion upgrades thereof.
2. Background of the Invention
Personal computers are becoming more prevalent in the work place with more and more people depending on their livelihoods from the use thereof. Advances in computer technology have created the ability and thus the demand for increased memory capacity, faster program computation, higher display resolution and faster presentation of information to the computer user. The demand for personal computers may also be attributable to its ease of use and adaptability to a multitude of tasks, both now and in the future.
The flexibility, adaptability and upgradability of the personal computer is in large part a function of the ease in which new developments in technology and functionality may be incorporated therein, both during manufacture at the factory and after purchase at the computer user's office or home. The personal computer market place has enjoyed an abundance of new and improved technologies largely because of an open system architecture and widely publicized interface standards.
The first of the personal computer interface standards was the Industry Standard Architecture (ISA) bus. The ISA bus utilizes an 8 bit input-output (I/O) bus having a maximum of 8 MHz data throughput. As the speed and sophistication of the personal computer system central processing unit (CPU) increased, a faster and higher data throughput capacity bus became necessary. The Extended Industry Standard Architecture (EISA) bus was developed to enable greater data throughput. The EISA bus utilizes a 32 bit I/O bus having a maximum of 8 MHz data throughput per 32 bit transfer.
The EISA bus, however, is still not sufficiently fast for computer operations requiring large amounts of digital data to be quickly transferred such as, for example, during hard disk access, communications, and video display. The transfer rate of the data over either the ISA or EISA buses is a limiting factor in the operation of the computer system. As an example, the speed at which a video display may be updated is determined by the transfer rate of the video data. Therefore, when a high resolution color display utilizing many colors needs to be updated, the amount of video data required takes an unacceptably long time to transfer over the ISA or EISA buses.
To alleviate this data transfer bottleneck, computer system manufacturers began utilizing a special data, address and control bus system that is closely coupled to the central processing unit (CPU) and random access memory (RAM). This bus operates at the same speed as the CPU, for example, 25-40 MHz. This high speed bus system is sometimes referred to as the "host local bus". By utilizing the host local bus, disk and high-speed video data transfers between memory or the CPU need no longer pass through either the ISA or EISA bus interfaces with their limited bandwidth. A standard for video controller interfaces utilizing the computer system local bus is being proposed by the Video Electronic Standards Association as a standard for advanced local bus video controllers (this standard referred to hereinafter as "VESA/VL").
Thus, a personal computer system may utilize either an ISA or EISA bus standard and a host local bus standard such as the VESA/VL bus standard. Utilizing a combination of these bus standards is desirable and appropriate for particular types of peripherals, so that each of these bus standards has utility for a particular purpose.
A personal computer system, in one conventional construction, is illustrated in FIG. 1. A computer housing 100 contains a power supply 102, floppy disk drive 104, hard disk drive 106, and motherboard 108. Referring to FIG. 2, the motherboard 108 has input-output connectors 202 adapted to receive either ISA or EISA peripheral device cards. Commonly owned U.S. Pat. No. 5,036,481, issued Jul. 30, 1991 and incorporated by reference herein, more fully illustrates the construction of a conventional personal computer system.
The computer motherboard 108 or system planar mounts horizontally in the system 100 housing. The motherboard 108 contains the CPU and support circuits thereto and provisions for connection of random access memory (RAM). More recent motherboards may incorporate provisions for a VESA/VL bus interface device such as interface logic circuits and VESA/VL connectors.
The motherboard 108 has a plurality of connectors 202 thereon for either ISA or EISA bus devices, and may be adapted to interface with a VESA/VL device (not illustrated). Support circuits are also needed to accommodate the various bus standards, and serial and parallel ports for the particular computer system. These support circuits are frequently referred to as "glue logic" and typically are located on the motherboard 108. Making provisions for future additions and upgrades in the computer system raises the complexity and cost of the computer system motherboard 108 and may doom the motherboard to early obsolescence if newer interface standards become popular. It is, therefore, an object of the present invention to provide an improved system and apparatus that allows easy upgradability without burdening the cost of a base computer system.